As a rule, a processing apparatus for photographic sheet material comprises several vessels each of which contains a treatment liquid, such as a developer, a fixer and a rinse liquid. As used herein, the term "sheet material" includes not only photographic material in the form of cut sheets, but also in the form of a web unwound from a roll. The sheet material to be processed is transported through these vessels in turn, by transport means such as one or more pairs of drive rollers, and thereafter optionally to a drying unit. The rollers are used in pairs, biased towards each other, between which the sheet material passes to act as a seal between treatment cells of the processing apparatus, that is to remove excess treatment liquid from the sheet as it passes from one treatment cell to the next. This reduces carry-over of treatment liquid and thereby reduces contamination and wastage. A good removal of processing liquid is also required to reduce the drying time of the sheet material after the last process bath, and hence to reduce the energy use.
A common construction of an apparatus for the wet processing of photographic sheet material includes at least one processing cell having an inlet and outlet together defining a sheet material path through the cell and a pair of rollers mounted between side plates in the cell and biased into contact with each other to form a nip there-between through which the sheet material path extends. Each of the rollers comprises a rigid core having a covering of elastomeric material secured to the core.
As described and shown in European patent application 95203464.3 (Agfa-Gevaert NV), the roller includes end parts comprising a wear resistant material vulcanised to the covering and in face-to-face sliding contact with an adjacent side plate.
Such a construction suffers from the disadvantage that after a period of use, the end parts of the covering suffer from wear, as a result of their sliding contact with the side plates, despite the incorporation of the wear resistant material. Such wear leads to leakage between the roller and the side plates. If this leakage is to be avoided, the roller must be replaced.